Densification of aerated powders using positive pressure

ABSTRACT

A process for increasing the bulk density of an aerated powder is provided. The powder is placed in a container. The container is then closed and the gas pressure within the container is increased to a level above atmospheric pressure and at a rate sufficient to cause the powder to compact before a substantial portion of said pressurization gas diffuses into said powder. In one embodiment, the process is utilized to increase the bulk density of an aerated, free-flowing titanium dioxide pigment. Apparatus for carrying out the process is also provided.

This application is a continuation application of co-pending applicationSer. No. 10/322,565 filed on Dec. 16, 2002.

BACKGROUND OF THE INVENTION

The present invention relates to methods and apparatus for increasingthe bulk density of aerated powders. By way of example only, theinvention can be utilized to increase the bulk density of highlyaerated, free-flowing inorganic metal oxide powders with considerablecommercial significance, for example, titanium dioxide pigments, complexmetal oxides of the type presently being employed in primary andsecondary rechargeable batteries (typically comprising lithium metaloxides) and blends of such complex metal oxides with various othercomponents of a cathode composition of a battery.

Handling and containing fine, highly aerated powders can be problematicin many respects. For example, filling a bag or other container tocapacity with a highly treated titanium dioxide pigment (for example,one designed for use in water-based latex paints) can be difficult toaccomplish in an efficient manner without first deaerating the pigment.Due to the relatively low bulk density of the pigment, the container cangenerally be filled to only 80 to 90% of its capacity. On standing, airentrapped in the pigment will slowly rise through the tortuous pathwaysdefined between gravitationally settling pigment particles, in theprocess increasing the bulk density of the pigment and allowingadditional pigment to be added to the container. However, in acontinuous manufacturing and packaging process, the additional time andhandling required to fill the container to capacity makes the processinefficient. Further, it can be difficult to impart a consistent,predetermined amount of pigment to each bag in a continuous baggingprocess. Similarly, filling a battery compartment or shell to capacityor with an exact amount of battery-active material (e.g., cathodematerial) can be difficult to achieve due to air entrapped in thematerial.

Various processes have been utilized to deaerate and compact afree-flowing powder. For example, the powder container has been placedon top of a device that allows the container to be shaken and/orvibrated as the container is filled. A similar technique involvesplacing a vibrating rod into the container in order to cause entrappedair to dissipate. Additional methods utilized in the past include acompression device for compressing the container and powder therein inorder to squeeze out air entrained in the powder, and placing a porouspipe connected to a vacuum system into the container during the fillingprocess to evacuate the entrained air. All of these processes haveserious drawbacks. For example, although removing entrained air with aporous pipe works for a short time, the pores in the pipe ultimatelybecome blocked due to the fine particle size of many powders.

One technique that has been used commercially over the years is vacuumdensification. In a vacuum densification process, the powder to bedeaerated is placed in a container that is connected to a vacuum source.A vacuum is then pulled to whatever level is desired. Upon attaining thedesired vacuum level, the valve controlling the vacuum source is closedand a second valve into the container is opened allowing the pressurewithin the container to rapidly equilibrate back to atmosphericpressure. This process causes the powder to compact.

Unfortunately, like the other powder deaeration processes utilizedheretofore, vacuum densification has its drawbacks. For example, vacuumsystems require an elaborate filter system and are generally somewhatexpensive to put in place. Many powder manufacturing plants do nototherwise have vacuum systems in place. Also, vacuum systems are limitedto atmospheric pressure (approximately 15 psig (1 kg/sq. cm, gauge)).

BRIEF SUMMARY OF THE INVENTION

In a vacuum densification process, the powder densifies to a smallextent as the pressure within the vacuum chamber decreases. However, itis the rapid in-flow of air into the evacuated container achieved byreleasing the vacuum that ultimately causes the deaerated material tocompact to a significant degree. If the vacuum is released at asufficient rate, the in-rush of air on top of the pigment is too fast toallow the air to diffuse back between the particles, thereby forcing thepigment into a smaller volume.

It has now been discovered that rapid pressurization of the gas (e.g.,air) in a closed vessel also causes a highly aerated powder within thevessel to become densified. Accordingly, the invention provides aprocess for increasing the bulk density of an aerated powder based onpositive pressure. As discussed below, the use of a positive pressuresystem to achieve the desired powder densification has many advantages.

In one aspect, the invention provides a process for increasing the bulkdensity of an aerated powder. In accordance with the process, the powderis placed in a container. The gas pressure in the area of the containercontaining the powder is then increased to a level above atmosphericpressure at a rate sufficient to cause the powder to compact before asubstantial portion of the pressurization gas diffuses into the powder.As explained below, the level above atmospheric pressure to which thegas pressure must be increased and the rate of increase required inorder to achieve a significant degree of powder compaction will varydepending upon the type of powder, the size of the container and otherparameters.

For example, in one application, the inventive process can be used toplace a predetermined volume of powder into a bag or other receptacle.The powder is placed in a container. The gas pressure is then increasedin the area of the container containing the powder to a level aboveatmospheric pressure at a rate sufficient to increase the bulk densityof the powder to a predetermined level. A predetermined amount of thecompacted powder is then removed from the container and placed in thereceptacle. This allows, for example, a consistent, predetermined amountof powder to be placed in each bag in a continuous bagging process.

In one embodiment, the gas pressure in the area of the containercontaining the powder is increased to a level above atmospheric pressureby injecting a gas into the container. The gas is injected into thecontainer at a rate sufficient to cause the powder to compact before asubstantial portion of the gas diffuses into the powder. A variety ofgases, including air, can be used, provided that the gas selected doesnot adversely react with the powder or otherwise negatively affecteither the process or the apparatus used to carry out the process.Preferably, the injection gas is an inert gas, air, nitrogen, oxygen,carbon dioxide or chlorine gas.

Examples of fine, highly aerated powders that can be densified inaccordance with the inventive process include inorganic metal oxidepowders such as inorganic pigments (e.g., titanium dioxide pigments) andbattery-active materials. Such battery-active materials include theinorganic metal oxide and metal phosphate powders used in primary andsecondary rechargeable batteries, for example, lithium metal oxides andlithium metal phosphates including those wherein the metal is vanadium,manganese, nickel, cobalt, iron or combinations of such metals. Thesebattery-active materials may or may not have lithium present in theircrystalline structure. The invention is particularly suitable fordensifying lithium vanadium oxides. Also, blends of battery-activematerials with other components for use in a cathode composition mayalso be densified in accordance with the inventive process, asexemplified below.

In another embodiment, the inventive process for increasing the bulkdensity of an aerated powder comprises placing the powder in acontainer, the container having a first end and a second end opposingthe first end. The gas pressure in the area of the container containingthe powder is then increased to a level above atmospheric pressure at arate sufficient to cause the powder to compact against the second end ofthe container before a substantial portion of the pressurization gasdiffuses into the powder. Next, the second end of the container isopened thereby causing the container to depressurize and the powder tobe expelled from the container through the second end of the container.

The invention also includes a process for preparing a slurry. Inaccordance with the process, the powder is first milled or otherwiseprocessed. The milling or other processing procedure typically causesthe powder to become aerated. Prior to allowing the powder to fullysettle, the bulk density of the powder is increased by deaerating thepowder. After the bulk density of the powder is increased, the powder isdispersed in a liquid medium. The deaeration step allows the powder tobe quickly dispersed in the liquid medium (i.e., the powder can bequickly dispersed into the liquid medium even though it has not beenallowed to fully settle). Unless the powder is deaerated (eithernaturally over time or in accordance with the invention), dispersinglarge amounts of the powder into a liquid medium in a timely manner canbe difficult to achieve. The powder is preferably deaerated inaccordance with the inventive positive pressure deaeration systemdescribed above.

For example, the above process can be used to disperse freshly fluidenergy milled titanium dioxide pigment into a suitable liquid, such aswater, to form a concentrated pigment slurry. The increased bulk densityof the pigment speeds up the slurry dispersion process by increasing therate at which the pigment will “wet” into the slurry. The concentratedpigment slurry can then be admixed into paint formulations and the likein a relatively quick and easy manner.

In another aspect, the invention includes apparatus for carrying out theinventive process. In one embodiment, the apparatus comprises acontainer for containing the powder under pressure, the container havinga first end and a second end opposing the first end. Pressurizationmeans are associated with the container for increasing the pressure inthe area of the container containing the powder to a level aboveatmospheric pressure at a rate sufficient to cause the powder to compactbefore a substantial portion of the pressurization gas diffuses into thepowder. In one embodiment, the pressurization means comprises means forinjecting a gas into the container, and a source of compressed gas.

In another embodiment, the inventive apparatus comprises: i) a cylinderwith first and second opposing ends defining an inlet and an outlet,respectively; ii) a rotary containment device positioned within thecylinder in a hub-and-spoke type arrangement whereby aerated powder canbe added through the inlet to powder containment areas defined byadjacent “spokes” within the cylinder; and iii) pressurization meanscomprising means for injecting a gas into the container, and a source ofcompressed gas. The device can be rotated such that powder in the powdercontainment areas is densified by the inputting of a pressurized gasthrough the pressurization means. The device can then be further rotatedsuch that densified powder is removed from the cylinder through theoutlet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are section views of a simple container illustrating thepositive pressure system of the invention.

FIG. 3 is a side elevation view illustrating one embodiment of theinventive apparatus.

FIG. 4 is a top view of the apparatus illustrated by FIG. 3.

FIG. 5 is a front schematic and partially sectional view illustratinganother embodiment of the inventive apparatus.

FIG. 6 is a graph corresponding to Example IV set forth below.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The invention provides a process for increasing the bulk density of anaerated powder. As used herein and in the appended claims, a powdermeans a solid, dry material of very small particle size ranging down tocolloidal dimensions (e.g., 0.01 microns). As used herein and in theappended claims, an “aerated” powder means a powder having air or someother gas entrapped among the particles forming the powder. The bulkdensity of a powder means the bulk density of the powder as determinedby the method described and shown in Example I below.

Referring now to FIGS. 1 and 2, the general mechanism of the inventiveprocess is illustrated and described. FIG. 1 illustrates a container 10containing an aerated powder 12 prior to densification. As shown by FIG.2, rapidly increasing the gas pressure in the area 14 of the container10 containing the powder 12 (in this case the area 14 is the wholeinterior of the container 10) to a level above atmospheric pressurecauses the powder to compact before a substantial portion of thepressurization gas diffuses into the powder. Without being limiting ofthe invention in any way, it is expected in mechanistic terms that apressure front or pressure wave (indicated by the dotted line 16) iscreated which forces the particles 12 together and forces out the airentrapped between the powder particles that would otherwise have to bedisplaced over time by the gravitational settling of the particles 12.

The compacted powder 12 can then be more efficiently processed. Forexample, in addition to being easier to handle, the powder can be moreefficiently packaged (e.g., packaging size can be standardized). Thecompacted powder 12 can also, for example, be more efficiently placedinto a shell or other vessel (e.g., a battery shell). In most batteryapplications, the more densely the active materials are compacted thegreater the charge density of the battery, i.e., compaction of thebattery-active materials results in a better battery.

In accordance with the inventive process, the powder is first placed ina container. The gas pressure in the area of the container containingthe powder is then increased to a level above atmospheric pressure at arate sufficient to cause the powder to compact before a substantialportion of the pressurization gas diffuses into the powder. Theparticular level above atmospheric pressure to which the gas pressuremust be increased and the corresponding rate of increase necessary toachieve a degree of compaction will vary depending upon the propertiesof the powder being densified, the amount of gas entrapped between thepowder particles, and on the container used to carry out the process. Ofcourse, the amount of gas pressure applied and the rate of increase inpressure will also depend upon the degree of compaction desired.Preferably and simply, the process involves increasing the pressure froman atmospheric pressure wherein the powder can be poured or flow bygravity into the container to a pressure greater than atmosphericpressure, which greater-than-atmospheric pressure can in turn be used tohelp expel the densified powder cleanly from the container intopackaging, for example.

For example, as shown by Example I below, in order to increase the bulkdensity of a freshly milled, hot (150 to 200° C.) latex paint gradetitanium dioxide pigment (“CR-813” marketed by Kerr-McGee Chemical, LLC)from 24.8 lbs/ft³ (0.40 g/cm³) to 41.7 lbs/ft³ (0.67 g/cm³) in a 3 litercylindrical steel vessel having a 15.3 cm inside diameter and a heightof 15.9 cm, the gas pressure in the area of the container containing thepigment (in this case the whole interior of the container) was increasedfrom 0 psig to 50 psig (3.5 kg/sq. cm) in approximately 10 to 15seconds. Similarly, as shown by Example V below, in order to increasethe bulk density of a freshly dried and vacuum-densified lithiumvanadium oxide battery-active material from 43.6 lbs/ft³ (0.70 g/cm³) to50.5 lbs/ft³ (0.81 g/cm³) in the same 3 liter cylindrical steel vessel,the gas pressure in the area of the container containing the pigment (inthis case the whole interior of the container) was increased from a fullvacuum condition (less than about 0.1 psia) to 90 psig (6.3 kg/sq. cm)in about 15 seconds.

Generally, after the desired compaction is obtained, the container isdepressurized and the compacted powder is removed from the container. Inone embodiment, the container in which the powder is densified alsoserves as the final or at least interim container (e.g., packaging) forthe product. In this event, of course, the compacted powder is notremoved from the container. In fact additional powder can be added tothe container and compacted in accordance with the invention, in one ormore additional cycles.

In one embodiment, the gas pressure in the area of the containercontaining the powder is increased to a level above atmospheric pressureby injecting a gas into the container. For example, as illustratedabove, gas can be injected into the container at a rate sufficient toincrease the overall pressure within the container as a whole to thedesired level within the desired amount of time in order to achievecompaction of the powder. The container is then depressurized and thecompacted powder is removed from the container.

The pressurization gas can be any gas, but should not adversely reactwith the powder or otherwise negatively affect either the process or theapparatus to carry out the process. The pressurization gas canconceivably be selected to be reactive with the powder in anadvantageous, desired way, in effect combining a reactive step in thepowder's preparation (or treatment) with densification. However, formost applications it is expected that the pressurization gas should benon-reactive with the powder and in the process and apparatus generally.In densifying a lithium metal oxide battery-active material or likemoisture- or oxygen-sensitive material, for example, an unreactive, drygas such as nitrogen is suitably used as the pressurization gas. In thecase of the densification of an aerated titanium dioxide powder,however, air is simply and preferably used as the pressurization gas.The gas can also conveniently be a gas that is otherwise present andreadily available (perhaps in an already pressurized condition) in anassociated process for making, treating or handling the aerated powder.For example, in the production of titanium dioxide pigment, chlorine gasis commonly utilized, generated and/or recycled. In an embodiment of theinvention, the chlorine gas is utilized as the gas injected into thecontainer to increase the gas pressure in the container and compact thepowder.

A variety of methods can be utilized to depressurize the container andremove the compacted powder from the container. For example, in oneembodiment, the powder is placed in a container having a first end and asecond end opposing the first end. The container is configured such thatincreasing the gas pressure in the area of the container containing thepowder to a level above atmospheric pressure causes the powder tocompact against the second end of the container. Once the powder iscompacted, the second end of the container is opened whereby thecontainer is depressurized and the compacted powder is expelled from thecontainer through the second end of the container.

Any aerated powder can be densified or compacted in accordance with theinvention. Examples of commercially significant aerated powders are thetitanium dioxide pigments and the complex metal oxides and metalphosphates used as battery-active materials, for example, those based onvanadium, manganese, nickel, cobalt, iron or a combination of suchmetals. Of particular interest are the lithium vanadium oxides, lithiumcobalt oxides, lithium nickel and lithium manganese oxides (includingthe many modified oxides based on each of these). Examples ofapplications in which densification of such aerated powders may bebeneficial include bulk bagging operations and operations to loadbattery-active materials into battery compartments of a limited volume.

One class of material to which the invention is particularly applicableis inorganic pigments. For example, due in part to a final fluid energymilling step, the bulk density of highly treated titanium dioxidepigment (for example, of a type designed for use in water-based latexpaints) is so low that it is not uncommon that the container can only befilled to 80-90 percent capacity. Typically, the bulk density of highlytreated, aerated titanium dioxide pigment is less than about 21.9lbs/ft³ (0.35 g/cm³). In accordance with the invention, the bulk densityof such a pigment can efficiently be increased to a level greater thanabout 49.9 lbs/ft³ (0.8 g/cm³).

The inventive densification process is particularly useful in connectionwith titanium dioxide pigments having bulk densities less than about21.9 lbs/ft³ (0.35 g/cm³). Preferably, in accordance with the presentinvention, the bulk density of a titanium dioxide pigment is increasedto a level greater than about 35 lbs/ft³ (0.56 g/cm³). More preferably,the bulk density of a titanium dioxide pigment is increased inaccordance with the invention to a level in the range of from about 35lbs/ft³ (0.56 g/cm³) to about 50 lbs/ft³ (0.80 g/cm³), even morepreferably from about 40 lbs/ft³ (0.64 g/cm³) to about 50 lbs/ft³ (0.80g/cm³).

In another aspect, the invention includes a process for preparing aslurry from an aerated powder. Due to the increased time required to“wet in” the powder into a liquid medium, preparing slurry from anaerated powder (and in particular, from a highly aerated powder) can bevery time consuming. Although aerated powders naturally gravitationallysettle over time, this adds another step between the final powderprocessing step and the slurry preparation process. In accordance withthe invention, the powder is first processed. For example, this mayentail a final powder milling (e.g., fluid energy milling) step whichtypically aerates the powder. Prior to allowing the powder to fullysettle, the bulk density of the powder is increased by deaerating thepowder. The densified powder is then wet in (dispersed) into the slurry.The resulting slurry can then be effectively and efficiently added toyet another medium such as a paint formulation.

Preferably, the powder is deaerated in accordance with the invention,namely placing the powder in a container under atmospheric conditions,increasing the gas pressure in the area of the container containing thepowder to a level above atmospheric pressure at a rate sufficient tocause the powder to compact before a substantial portion of thepressurization gas diffuses into the powder and removing the compactedpowder from the container.

In the titanium dioxide pigment industry, significant amounts of pigmentare sold in a slurry format. These slurries are typically made at solidslevels ranging from about 65% to about 76% by weight. To achieve thesehigh solids levels, various dispersants are added to facilitate bothrapid “wet-in” and to form a stable dispersion. The term “wet-in” refersto the displacement of the air surrounding the particles with a liquid.In highly aerated powders, occluded air can significantly increase theoverall time required to complete the “wet-in” step. By densifying thepigment prior to initiating the dispersion process, the “wet-in” timecan be significantly reduced. For example, the “wet-in” time associatedwith dispersing a titanium dioxide pigment into water to form a slurryis, by the present process, preferably reduced by at least 10 percent,more preferably at least 20 percent and most preferably by at least 30percent in comparison to the amount of “wet-in” time required for thesame pigment under the same conditions but wherein the pigment has onlybeen allowed to deaerate naturally and with settling of the pigment.

The invention is also particularly useful for increasing the bulkdensity of battery-active materials and of compositions containing suchmaterials, as used for making the cathode of a primary or secondaryrechargeable battery, for example. It will be appreciated in this regardthat with the advent of increasingly smaller yet more sophisticatedhand-held electronic devices, the batteries used in such devices must becapable of delivering a correspondingly greater amount of electricalenergy yet occupy a smaller space than in earlier such devices. Thepresent invention addresses this need and helpfully enables a greateramount of a given battery-active material to be employed in theincreasingly smaller, fixed volume battery containers or shells that arerequired. Preferably, by the process of the present invention, the bulkdensity of a battery-useful composition containing a battery-activematerial (or mixture of such materials) can be increased by at leastabout 10 percent, more preferably by at least about 15 percent and mostpreferably by at least about 30 percent from the bulk density of thesame composition without any positive pressure densification ordeaeration having been used.

The inventive process does not necessarily require sophisticatedapparatus; any closed container should work provided the materials ofconstruction are capable of sustaining both the desired operatingpressures and a corrosive environment if corrosive materials areinvolved.

Referring now to the drawings, and particularly to FIGS. 3 and 4, onepreferred embodiment of the inventive apparatus, generally designated bythe reference numeral 20, is described. The apparatus 20, an air-lockassembly, can be utilized to increase the bulk density of any powder.The particular form of the apparatus 20 is not critical. In fact, thereare a variety of spherical disk valves and air lock assemblies that arecommercially available and can be modified for use in connection withthe invention. The particular apparatus shown by FIGS. 3 and 4 is aGEMCO® Spherical Disc Valve or Airlock that has been modified inaccordance with the invention.

The apparatus 20 is positioned in the vertical mode and comprises acontainer 22 for containing a powder under pressure. For example, in acontinuous titanium dioxide manufacturing process, titanium dioxidepigment can be fed directly into the container 22 from a titaniumdioxide separator (not shown).

The container 22 includes a first end 30 and an opposing second end 32.Pressurization means 34 are associated with the container 22 forincreasing the gas pressure in the area 36 of the container 22containing the powder to a level above atmospheric pressure and at arate sufficient to cause the powder to compact before a substantialportion of the pressurization gas diffuses into the powder.

In one embodiment, pressurization means 34 comprise injection means 38for injecting a gas into the container 22, and a source of gas 40 (e.g.,compressed gas). The injection means 38 includes a conduit 42 extendingfrom the source 40 into the container 22 and a corresponding valve 44.The source 40 of compressed gas includes a suitable container 46. Thepressure of the gas in the container 46 is sufficient to force the gasthrough the conduit 42 into the container 22 at a rate sufficient toincrease the gas pressure in the container 22 to the desired level andwithin the desired amount of time.

The first end 30 of the container 22 includes an inlet 48 for allowingthe powder to be added to the container (the inlet includes a flange 48a for connection to the feed supply). The second end 32 of the container22 includes an outlet 50 for allowing the powder to be discharged fromthe container into a bag or other receptacle (not shown) (the outletincludes a flange 50 a for connection to the receptacle). The containerfurther includes a first valve 54 for opening and closing the inlet 48and a second valve 56 for opening and closing the outlet 50. Asillustrated, the valves 54 and 56 are conventional sliding knife gatevalves, which are automatically operated by corresponding valve motors58 a and 58 b as known to those skilled in the art (e.g., the motors canbe electrically or pneumatically operated; a programmable logiccontroller can be included to control cycle time). The valves 54 and 56open and close very quickly allowing rapid filling and discharge fromthe container. One or more pressure valves 60 can be associated with thecontainer 22 for indicating the pressure within the container 22.

In operation of the apparatus illustrated by FIGS. 3 and 4, the firstvalve 54 is opened and the powder to be densified is gravity fed intothe container 22 through the inlet 48. The valve 56 remains fullyclosed. The powder falls and piles up against the valve 56. Once thecontainer 22 is filled to the desired level, the valve 54 is closed. Thevalve 44 is then opened to inject pressurization gas from the source ofgas 40 into the container 22. The pressurization gas within the sourceof gas 40 is compressed such that it is injected into the container 22at a rate sufficient to increase the gas pressure in the container tothe desired level, i.e., to a level above atmospheric pressure at a ratesufficient to cause the powder to compact whereby the powder iscompacted or densified against the valve 56 of the container 22 before asubstantial portion of the pressurization gas diffuses into the powder.Once the powder has been compacted as desired, the valve 56 is openedwhereby gravity together with the increased gas pressure within thecontainer 22 causes the powder to completely eject from the container22. This is an added benefit of the invention, particularly incircumstances where the cohesive characteristics of some powders maycause these powders to tend to stick to the walls of the container 22and not be easily removed to a separate package, for example. Theincreased gas pressure in the container 22 can help overcome thetendency of such powders to stick to the walls of the container 22. Thecompacted powder is directly ejected into a bag or other type of productreceptacle (not shown). Preferably, no additional mechanical device isrequired to effect the discharge.

Referring now to FIG. 5, yet another embodiment of the inventiveapparatus for increasing the bulk density of a powder is illustrated.The apparatus in this embodiment, which is generally designated by thereference numeral 70, includes a cylinder 72, a rotary containmentdevice 74, rotating means 76 (represented by dotted lines) for turningthe rotary containment device within the cylinder, and pressurizationmeans 78 associated with the cylinder. A powder 80 is fed from a feedcontainer 82 into the cylinder 72 and ultimately from the cylinder intoan end-container (e.g., a bag) 84.

The cylinder 72 includes a first end 90 containing an inlet 92, a secondend 94 opposing the first end and containing an outlet 96 and a wall 98.The inlet 92 includes a first valve 100. The outlet 96 includes a secondvalve 102. The rotary containment device 74 is positioned within thecylinder 72. The rotary containment device includes a hub 110 and threepairs of opposed blades, 112A and 112B, 114A and 114B and 116A and 116B,respectively, attached to the hub. The blades 112A and 112B, 114A and114B and 116A and 116B create six powder containment areas 120A through120F within the cylinder 72. The rotary containment device 74 is capableof turning within the cylinder 72 such that each of the powdercontainment areas 120A through 120F rotate to a first position 122within the cylinder adjacent the inlet 92 whereby non-compacted powder80 can be added to the area, a second position 124 within the cylinderadjacent the wall 98 of the cylinder whereby powder 80 in the area canbe compacted, and a third position 126 adjacent the outlet 96 wherebycompacted powder 80 can be ejected from the area into the end-container84.

The rotating means 76 includes a motor 130 (represented by dotted lines)and shaft 132. The shaft 132 is attached at one end to the motor 130 andthe other end to the hub 110. The motor 130 rotates the shaft 132, whichin turns rotates the rotary containment device 74.

The pressurization means 78 associated with the cylinder 72 function toincrease the gas pressure within each of the powder containment areas120A through 120F of the rotary containment device 74 so that the powderwithin the area is compacted or densified when the area is in the secondposition 124. The gas pressure within each of the powder containmentareas 120A through 120F is increased to a level above atmosphericpressure and at a rate sufficient to cause the powder within the area tocompact before a substantial portion of the pressurization gas diffusesinto the area. The pressurization means 78 include a pulsed air pressurecontrol system 140, a main gas conduit 142, a filter and vent system 144and a cleanout system 146. A first end 148 of the main gas conduit 142is attached to the pulsed air pressure control system 140. A second end150 of the main gas conduit 142 extends through the wall 98 of thecylinder 72 and is positioned in each of the powder containment areas120A through 120F when the area is in the second position 124.

The filter and vent system 144 includes a valve 154, pressure gauge 156and a bag-type filter 158. A first branch 160 of the main gas conduit142 extends into the filter 158. The filter and vent system 144 allowsgas to be vented from the pressurization means 78 as necessary.

A second branch 164 of the main gas conduit 142 extends into thecleanout system 146. The cleanout system 146 includes a valve 166 andallows any particles that become entrapped in the pressurization means78 to be removed from the pressurization means.

In operation, powder 80 to be compacted is placed in the feed container82. The rotating means 76 is operated to rotate the rotary containmentdevice 74 in a counterclockwise direction within the cylinder 72 at thedesired rate; i.e., a rate such that a proper amount of powder 80 willbe fed into each of the powder containment areas 120A through 120F whenthe area is in the first position 122, and to allow the powder 80 in thearea to be sufficiently compacted when the area is in the secondposition 124. The first valve 100 is then opened allowing non-compactedpowder 80 to fill each of the powder containment areas 120A through 120Fwhen the area is in the first position 122. As the rotary containmentdevice rotates, each of the powder containment areas 120A through 120Fmoves from the first position 122 to the second position 124. When inthe second position 124, the pressurization means 78 operates toincrease the gas pressure within the corresponding powder containmentarea to the desired level above atmospheric pressure at a ratesufficient to cause the powder in the area to compact before asubstantial portion of the pressurization gas diffuses into the powder.Rotation of the rotary containment device 74 causes each of the powdercontainment areas 120A through 120F to also rotate from the secondposition 124 to the third position 126. When a powder containment areais in the third position 126, the compacted powder therein falls fromthe area through the second valve 102 and outlet 96 into the endcontainer or bag 84. Continuous operation of the device allows powder tobe continuously densified in accordance with the invention.

The pressurization means 78 operates to increase the gas pressure withineach of the powder containment areas 120A through 120F as follows: Airis injected into the main gas conduit 142 by the pulsed air pressurecontrol system 140. The air is conducted by the main gas conduit 142into the powder containment area in the second position 124. The airflows from the second end 150 of the main gas conduit 142 into the areain the second position. The pulsed air pressure control system 140causes the air to be conducted through the main gas conduit 142 at arate sufficient to increase the gas pressure in the powder containmentarea in the second position 124 to the desired level above atmosphericpressure and at the desired level and at the desired rate, i.e., a ratesufficient to cause the powder within the area to compact before asubstantial portion of the pressurization gas diffuses into the powder.

The filter and vent system 144 allows air to be vented from the systemwhen the pressure in the system, as indicated by the pressure gauge 156,exceeds the desired limit. The valve 154 is opened allowing excess airto travel through the first branch 160 of the conduit 142 into thefilter 158 and ultimately into the atmosphere. The filter 158 catchesany particles present in the vent gas.

The cleanout system 146 allows any powder that accumulates in the maingas conduit 142 or other parts of the pressurization means 78 to beremoved from the system. The valve 146 is opened allowing air andparticles in the main gas conduit 142 to enter the second branch 164 ofthe conduit where it is conducted through the valve and collected in anappropriate manner.

The following examples are provided to further illustrate theeffectiveness of the inventive method and composition.

EXAMPLE I

A set of experiments was carried out to verify that rapid pressurizationof a closed vessel containing a highly aerated powder causes the powderto densify or compact (i.e., forces the powder into a smaller volume).All four combinations of rapid and slow pressurization and rapid andslow depressurization were evaluated. Bulk density values weredetermined in a conventional manner using a “HOSOKAWA Micron PowderTester, Model PT-E,” by filling and leveling a 100 cubic centimeter cupwith the powder, attaching an extension piece on top of the cup andfilling the extension piece as well. The filled cup and extension piecewere tapped for 180 seconds at a 60 cycle frequency, with the additionof powder as necessary to keep the level of the powder above the top ofthe cup. At the conclusion of the tapping cycle, the extension wascarefully removed and the cup leveled to remove excess powder. Theweight difference between the filled, tapped and leveled cup and theempty cup in grams, divided by the 100 cubic centimeter volume of thecup, provided the sample bulk density in grams per cubic centimeter.

The powder used in the tests was a highly aerated, latex paint gradetitanium dioxide pigment (“CR-813” pigment sold by Kerr-McGee Chemical,LLC). First, the pigment was milled in a fluid energy mill usingsuperheated steam which aerated the pigment and raised the temperatureof the pigment to approximately 150-200° C. The bulk density of thispigment, prior to testing, was 24.8 lbs/ft³ (0.40 g/cm³). Approximately500 grams of the hot pigment were then placed into a 3 liter,cylindrical steel vessel (15.3 cm inside diameter, 15.9 cm in height)having a removable top. The top of the vessel was then attachedsecurely. A first valve attached to the top of the vessel and connectedto a compressed air line was opened thereby causing the vessel topressurize from zero psig to approximately 50 psig (3.5 kg/sq. cm,gauge) within 10 to 15 seconds. Once the pressure reached the level ofapproximately 50 psig, the first valve was closed and a second valve,also attached to the top of the vessel, was opened. Opening of thesecond valve allowed the vessel to equilibrate back to atmosphericpressure in approximately 10 to 15 seconds. The top of the vessel wasthen removed and the pigment was recovered from the vessel. The bulkdensity of the recovered pigment (Sample 1A) was determined to be 41.7lbs/ft³ (0.67 g/cm³). Thus, the bulk density of the pigmentsubstantially increased, specifically by 68 percent.

Next, the experiment described above was repeated using the sameprocedure and a fresh sample of the same hot pigment. The only exceptionwas that the pressure in the vessel was allowed to climb to 50 psig over3 minutes, as opposed to 10 to 15 seconds, and was allowed toequilibrate back to atmospheric pressure over a one minute time frame,as opposed to a 10 to 15 second time frame. The bulk density of therecovered pigment (Sample 1B) was determined to be 26.6 lbs/ft³ (0.43g/cm³), almost the same as the starting material.

A third test was carried out, also utilizing the same equipment andprocedure and a fresh sample of the same hot pigment. In this test,however, the vessel was pressurized rapidly but depressurized slowly.Specifically, the pressure in the vessel was allowed to climb toapproximately 50 psig over 10 to 15 seconds and then allowed toequilibrate back to atmospheric pressure over approximately a one-minutetime frame. The bulk density of the recovered pigment (Sample 1C) wasdetermined to be 41.7 lbs/ft³ (0.67 g/cm³), which is equal to the levelachieved in connection with Sample 1A.

A fourth example was carried out to illustrate the effect of initiallypressurizing the vessel slowly but depressurizing the vessel rapidly.Again, the test was carried out using the same equipment and procedureas above and a fresh sample of the hot pigment. In this test, however,the pressure was allowed to climb to approximately 50 psig over threeminutes and to then dissipate over a 30-second time frame. The bulkdensity of the recovered pigment (Sample 1D) was determined to be 29.7lbs/ft³ (0.47 g/cm³), which was only slightly higher than the startingmaterial.

The results of the above experiments unequivocally show that it is rapidpressurization of the vessel that is responsible for significantlydensifying the pigments.

EXAMPLE II

The pigment densified in accordance with Example I (Sample 1A) wastested in paint formulations to verify that densification accomplishedby means of the present invention does not negatively impact the opticalproperties of the pigment. A paint formulation containing pigment Sample1A (having a bulk density of approximately 41.7 lbs/ft³ (0.67 g/cm³))and a paint formulation including the pigment prior to being treated inaccordance with the inventive process (having a bulk density of 24.8lbs/ft³ (0.40 g/cm³)) (the “untreated pigment sample”) were tested.

The paint formulations were standard latex paint formulations, designedfor interior architectural applications. The formulations were formed byincorporating the pigment samples in portions of a freshly preparedpolyvinyl acetate latex emulsion. In each formulation, the amount of thepigment sample incorporated into the emulsion was 60% by volume based onthe total volume of the emulsion.

The resulting paint formulations were first applied to black glassplates and white cards. The Y reflectance values of the dried paintfilms were measured with a HunterLab Color Difference Meter as known tothose skilled in the art. These readings, in combination with measuredfilm weights, were used to calculate the scatter value, expressed ashiding power in square feet per pound of pigment.

Next, a fixed amount of a carbon black tint was added to a portion ofeach paint formulation to form a tinted paint sample for eachformulation. The four paint samples were mixed thoroughly. Drawdowns ofall four paint samples and of corresponding controls were then made onstandard LENETA™ charts. From these drawdowns readings from theHunterLab Color Difference Meter were obtained to enable tint strengthcalculations to be made. All methods and calculations were carried outin accordance with ASTM D2805 and D2745, respectively. The results areshown in Table 1 below. TABLE 1 Optical Properties of Paint FormulationsPaint with Untreated Paint with Test Method Pigment Sample PigmentSample A Hiding Power (sq. ft/lb of 221 222 pigment) Tint Strength (% ofStandard) 106.6 108.6The results of the tests show that there was no deterioration in theperformance of the pigment densified in Example I whether in terms ofhiding power (dryhide) or tint strength.

EXAMPLE III

The effect of varying the densification pressure on the bulk density ofthe pigment was demonstrated. The pigment used in this series of testswas a highly aerated, latex paint grade titanium dioxide pigment(“CR-813” sold by Kerr-McGee Chemical, LLC). Six samples of the pigment,including a control, were tested.

First, five of the six samples of the pigment were densified utilizingthe same process, apparatus and equipment described in Example I. Exceptfor the densification pressure utilized, the test parameters in eachexperiment were the same. In each test, the vessel was rapidlypressurized to the target pressure level within approximately 3-5seconds. Upon obtaining the target pressure level, the vessel wasallowed to equilibrate back to atmospheric pressure over approximately10-15 seconds. The densification pressures used in the densificationprocess ranged from 15 psig (1 kg/sq. cm) to 72 psig (5 kg/sq. cm). Thebulk density of each pigment sample, including the control sample, wasdetermined as in Example I.

Paint formulations utilizing the control sample as well as the fivesamples densified in accordance with the inventive process were thenmade. The same formulations, equipment and procedure described inExample II were utilized. The hiding power and tint strength of thesamples were then measured utilizing the same procedure described inExample II. The results of the tests are shown in Table 2 below. TABLE 2Effective of Densification Pressure on Optical Properties of PaintFormulations Pressure Bulk Density Hiding Power Tint Strength Samplepsig lbs/ft³ (sq. ft./lb Pigment) (% of Standard) 3A 0 24.9 213 106.8 3B15 27.7 213 105.4 3C 30 35.4 213 106.9 3D 45 39.0 214 106.4 3E 60 40.0213 104.6 3F 72 42.8 213 104.9

The bulk density measurements demonstrate that the bulk density of thepigment increases with increasing densification pressure. Opticalproperties as measured by hiding power and tinting strength show nochange over the range of densification pressures evaluated. The testsshow that the pigment can be densified very significantly (from 24.9 to42.8 lbs/ft³, which represents an increase of almost 72%) withoutaffecting the optical properties of paint formulations formed therewith.

EXAMPLE IV

A test was carried out to illustrate the beneficial effects that theinventive densification process and apparatus have on the rate that apowder can be dispersed into an aqueous medium. The pigment used in thetest was the same pigment described in Example III above. The pigmentwas fresh from a fluid energy milling step of the pigment manufacturingprocess. Bulk density values were determined as in Example I.

Two samples were made, the first to be used as a control. The secondsample was densified utilizing the same procedure and apparatusdescribed in Example I; in this case pressurization was to approximately50 psig within 3-5 seconds and depressurization was carried out over atime period of 10-15 seconds. Bulk density measurements showed that thecontrol had a value of 27.1 lbs/ft³ (0.43 g/cm³) and the densifiedsample had a value of 40.0 lbs/ft³ (0.64 g/cm³, for an increase ofalmost 48%).

Next, using a DISPERMAT™ Model AE3C available from Byk-Gardner, U.S.A.,equipped with torque sensing capability, slurries were made from each ofthe two pigment samples. The technique involved adding 775 grams of thepigment sample being tested to 370 grams of water and a proprietaryblend of dispersants. All operational parameters such as speed andtemperature were maintained at a constant level. The method of additionof the pigment to the aqueous medium was such that the only ratelimiting factor was the ability of the titanium dioxide to “wet-in” tothe slurry.

The results are demonstrated by FIG. 6 of the drawings of thisapplication. FIG. 6 includes time-torque plots showing both the sampledensified in accordance with the invention and the control sample. Asshown, the pigment sample densified in accordance with the inventionreached a steady state torque 50 to 52 seconds before the control. Thus,the ability of a powder to be dispersed in an aqueous medium can besubstantially enhanced by densifying the powder in accordance with theinvention.

EXAMPLE V

A pressure densification test was run on a cathode composition comprisedof a lithium vanadium oxide battery-active material and about 5 percentby weight of a combination of graphite and carbon black, whichcomposition had been previously dried and densified under vacuum only. Asample was placed into the same 3 liter steel test cylinder described inExample I and full vacuum (to less than 0.1 psia) was applied. Thecylinder was then pressurized to 90 psig (6.3 kg/sq. cm) in about 15seconds with nitrogen. The packed bulk (tap) density increased from anominal 43.6 lbs/ft³ (0.70 g/cm³) to 50.5 lbs/ft³ (0.81 g/cm³), about a15% increase in density.

EXAMPLES VI THROUGH VIII

For Examples VI through VIII, similar pressure densification tests wereconducted on two samples each of three additional battery-useful,cathode compositions, all comprised of lithium vanadium oxidebattery-active material, carbon black and graphite. The compositions ofthe samples used for Examples VI and VII were the same, while thecomposition for Example VIII used a somewhat greater proportion ofgraphite as compared to carbon black.

In contrast to Example V, a vacuum was not applied initially, so thatpressurization took place with nitrogen from atmospheric pressure to 90psig over about 15 seconds. The valve to the container was then opened,and the pressure rapidly released over a span of about 5 seconds. Alsoin contrast to previous examples, in Examples VI through VIII thesamples were subjected to the same densification procedure twice more toachieve maximum densification, before the packed bulk (tap) density wasdetermined. Results are presented below in Table 3, with the densitiesbeing expressed in grams per cubic centimeter: TABLE 3 Density afterSample Density Densification Avg. Percent Densification 1A 0.72 0.7710.2 1B 0.67 0.76 2A 0.59 0.70 16.8 2B 0.60 0.69 3A 0.61 0.84 33.9 3B0.63 0.82Thus, significant improvements in the bulk densities of the samples wereachieved.

1. A process for increasing the bulk density of an aerated powder,comprising: placing said powder into a container, said container havinga first end and a second end opposing said first end; increasing the gaspressure in the area of said container containing said powder to a levelabove atmospheric pressure at a rate sufficient to cause said powder tocompact against said second end of said container before a substantialportion of said pressurization gas diffuses into said powder; openingsaid second end of said container whereby said container isdepressurized and said powder is expelled from said container throughsaid second end of said container.
 2. The process of claim 1 whereinsaid powder is placed directly into said container.
 3. The process ofclaim 1 wherein said gas pressure in the area of said container isincreased to a level above atmospheric pressure for less than 30seconds.
 4. The process of claim 1 wherein said gas pressure in the areaof said container containing said powder is increased to a level aboveatmospheric pressure by injecting a gas into said container.
 5. Theprocess of claim 4 wherein said gas injected into said container isselected from the group consisting of an inert gas, air, nitrogen,oxygen, carbon dioxide and chlorine.
 6. The process of claim 1 whereinsaid powder is an inorganic metal oxide.
 7. The process of claim 1wherein said powder is a titanium dioxide pigment.
 8. The process ofclaim 7 wherein the bulk density of said titanium dioxide pigment isincreased to a level greater than about 35 lbs/ft³.
 9. The process ofclaim 7 wherein the bulk density of said titanium dioxide pigment isincreased to a level in the range of from about 40 lbs/ft³ to about 50lbs/ft³.
 10. The process of claim 1 wherein said powder comprises abattery-active material.
 11. The process of claim 10 wherein saidbattery-active material is selected from the group of metal oxides andmetal phosphates wherein said metal is vanadium, manganese, nickel,cobalt, iron or a combination thereof.
 12. The process of claim 10wherein said battery-active material is selected from the group oflithium metal oxides and lithium metal phosphates wherein said metal isvanadium, manganese, nickel, cobalt, iron or a combination thereof. 13.The process of claim 10 wherein the bulk density of said battery-activematerial is increased by at least about 10 percent.
 14. The process ofclaim 10 wherein the bulk density of said battery-active material isincreased by at least about 15 percent.
 15. A process for increasing thebulk density of an aerated powder, comprising: placing said powder in acontainer, said container having a first end and a second end opposingsaid first end; increasing the gas pressure in the area of saidcontainer containing said powder to a level above atmospheric pressure,other than by decreasing the volume of the area of the containercontaining said powder, at a rate sufficient to cause said powder tocompact against said second end of said container before a substantialportion of said gas diffuses into said powder; opening said second endof said container whereby said container is depressurized and saidpowder is expelled from said container through said second end of saidcontainer.
 16. The process of claim 15 wherein said gas pressure in thearea of said container containing said powder is increased to a levelabove atmospheric pressure by injecting a gas into said container. 17.The process of claim 16 wherein said gas injected into said container isselected from the group consisting of an inert gas, air, nitrogen,oxygen, carbon dioxide and chlorine.
 18. The process of claim 15 whereinsaid powder is an inorganic metal oxide.
 19. The process of claim 15wherein said powder is a titanium dioxide pigment.
 20. The process ofclaim 19 wherein the bulk density of said titanium dioxide pigment isincreased to a level greater than about 35 lbs/ft³.
 21. The process ofclaim 15 wherein said powder comprises a battery-active material. 22.The process of claim 21 wherein said battery-active material is selectedfrom the group of metal oxides and metal phosphates wherein said metalis vanadium, manganese, nickel, cobalt, iron or a combination thereof.23. The process of claim 21 wherein said battery-active material isselected from the group of lithium metal oxides and lithium metalphosphates wherein said metal is vanadium, manganese, nickel, cobalt,iron or a combination thereof.
 24. The process of claim 21 wherein thebulk density of said battery-active material is increased by at leastabout 10 percent.
 25. An apparatus for increasing the bulk density of apowder, comprising: a container for containing said powder underpressure; and pressurization means associated with said container forincreasing the gas pressure in the area of said container containingsaid powder, other than by decreasing the volume of the area of thecontainer containing said powder, to a level above atmospheric pressureat a rate sufficient to cause said powder to compact before asubstantial portion of the gas in the area of said container containingsaid powder diffuses into said powder, said container having a first endincluding an inlet for allowing said powder to be added to saidcontainer and a second end opposing said first end, said second endincluding an outlet for allowing said powder and said pressurized gas tobe removed from said container, said container comprising a first valvefor opening and closing said inlet and a second valve for opening andclosing said outlet.
 26. The apparatus of claim 25 wherein saidpressurization means comprises: means for injecting a gas into saidcontainer; and a source of gas.
 27. The apparatus of claim 26 whereinsaid source of gas provides a gas selected from the group consisting ofan inert gas, air, nitrogen, oxygen, carbon dioxide and chlorine gas.28. The apparatus of claim 26 wherein said pressurization means causessaid powder to compact against said outlet when said outlet is closedand eject from said container when said outlet is opened.
 29. Anapparatus for increasing the bulk density of a powder, comprising: acylinder, said cylinder having a first end and a second end opposingsaid first end, said first end containing an inlet and said second endcontaining an outlet; a rotary containment device positioned within saidcylinder, said rotary containment device including: a hub; one or morepairs of opposed blades attached to said hub, each of said pairs ofopposed blades creating two powder containment areas within saidcylinder, said rotary containment device being capable of turning withinsaid cylinder such that each of said powder containment areas rotate toa first position within said cylinder adjacent said inlet whereby powdercan be added to said area, a second position within said cylinderadjacent said wall of said cylinder whereby powder in said area can becompacted, and a third position within said cylinder adjacent saidoutlet whereby powder in said area can be ejected from said area; androtating means for turning said rotary containment device within saidcylinder; and pressurization means associated with said cylinder forincreasing the gas pressure within said each of said powder containmentareas of said rotary containment device to a level above atmosphericpressure when said area is in said second position at a rate sufficientto cause the powder within said area to compact before a substantialportion of the pressurization gas diffuses into the powder.
 30. Theapparatus of claim 29 wherein said rotary containment device includesthree pairs of opposed blades attached to said hub.
 31. The apparatus ofclaim 29 wherein said pressurization means comprises: means forinjecting a gas into said powder containment areas; and a source ofcompressed gas.